The period between the discovery of the insecticidal properties of Dichlorodiphenyltrichloroethane (DDT) by Paul Muller and the publication of Silent Spring by Rachel Carson played a significant role in establishing chemical agriculture in the global food production system. The use of synthetic (artificial) pesticides and the so-called green revolution rooted the flow of synthetic chemicals in the food chain. Spraying chemical insecticides has become the most popular approach to reducing insect-pest populations, currently due to their easy availability, instant results, and cheaper products. The Stockholm Convention banned persistent organic pollutants (POPs), and several countries have restricted different pesticides. However, the use and misuse have remained relatively high, and the permitted pesticides are also not in harmony with the agroecological balance. Long-term environmental deterioration, increase in cultivation expenses, and adverse effects on soil, water, air, and plant biomass that multiply every year, are certain and inevitable.

The use of synthetic inputs can be discouraged by organic pest management techniques. Insect pest management in organic systems involves adopting scientific and ecologically sound techniques specified by national and international standards. The standards forbid synthetic insecticides and genetically modified organisms (GMOs) and rely upon various cultural practices, habitat manipulation, deployment of biocontrol agents and approved insecticides. The methods and tools that are permitted in organic production systems are not yet well defined by law, and thus regional variations exist.

Microbial pest control

There is a long history of intricate interactions between insects and microorganisms. In the natural ecosystem, the insect-pest population is continuously suppressed without human intervention. They are attacked by soil-dwelling microbes living close to the insect population, like entomopathogens. Entomopathogens are infectious microorganisms that invade and multiply in one insect and spread to infect other insects, which cover non-cellular (viruses), prokaryotes (bacteria), and eukaryotes (fungi and protists) to multicellular nematodes. The purposeful utilisation of such organisms by humans for pest control mechanisms is the essence of microbial pest control. Microbial control strategies aim to suppress a pest population below the economic injury level (EIL). The objective is accomplished by increasing disease prevalence in a target population.

Fungi are among the most frequently seen pathogens, inflicting diseases on insects in the wild. As early as 1835, Agostino Bassi demonstrated that a microorganism (fungus), Beauveria bassiana, was the causal agent of the white muscardine disease of the silkworm and that this disease could be transmitted from one insect to another. Bassi thus assumed that these microorganisms might be used to control pests on cultivated crops. In the late 18th century, while working to develop the control measure of cereal cockchafer, Elie Metchnikoff in Russia discovered a fungus attacking this pest, which he called the “green muscardine” and described the agent as Entomophthora anisopliae. The fungus is now called Metarhizium anisopliae. The disease caused by the fungus on insects is popularly called the “green muscardine disease.”

Beauveria bassiana and Metarhizium anisopliae can be found in soils of all continents, including the climatic extremes, except Antarctica. The group is best known for its ability to kill a wide spectrum of insects and infect hundreds of host species from most insect orders. It can also live on for an extended period in a saprotrophic environment in the soil. As a rule, a fungus with a broader host range is often facultative, meaning it can derive nutrients from non-hosts sources, for survival. This is a major benefit humans can utilise from these fungi because they can be extracted from their natural habitat, i.e., soil, and multiplied in-vitro conditions, providing suitable, artificially prepared media for storage and future use. Moreover, it is non-poisonous to mammals, including humans and is selective against the target insects and safe for most non-target species. It protects pollinators, parasitoids, predators, and other industrial insects such as honey bees. The diversity of beneficial insects is thus protected, ultimately enhancing the ecological balance.

Applying an ultra-low volume to the plant surface or insect environment is a great approach to introducing a fungus inoculum with a high concentration of inoculum, and spraying is also very much similar to conventional pesticide spray. Compared to synthetic insecticides, this procedure is time-consuming and has a slow death rate. However, it is not always necessary to completely kill the host to stop damage; slight inactivation in the insect's physiology can also hamper its feeding performance and fecundity, which ultimately helps lower the level of damage. Additionally, when conditions are favourable, fungal infections can cause dramatic epizootic diseases that wipe out populations of specific insects.

Challenges and way forward

The growth of organic pest management in Nepal is still in its infancy. Our organic soil is the prime reservoir of insecticides, but we are behind in exploration, awareness, research, and development. Farmers are unaware of laboratory facilities and emerging technologies for organic pest management. Limited producers manufacture some fungal products, but their efficiency is not good. Hence, the local strains of our own soil must be searched for and produced to gain maximum efficacy. The field of epizootiology should be developed by highlighting and integrating it into graduate and undergraduate curricula.

Silent Spring inspired a modern environmental movement, but the human and environmental health concerns depend on how democracies and liberal economies operate. Despite the extensive exploration and utilisation possibilities of several microorganisms such as Beauveria and Metarhizium, the domination of profit-oriented commercial farms and corporate agriculture overshadow the organic, agroecological, and biodynamic pest management, which not only exploit nature, but also kill the subsistence producers, small peasantry, and consumers on a global scale. Pest control techniques should be incorporated into a more comprehensive pest management approach. The emphasis should be on pest control interventions that can produce pest control benefits across a wide range of pests suitable for diverse crops and cropping systems.